1. Field of the Invention
The present invention relates generally to a multi-hop relay wireless communication system, and in particular, to an apparatus and method for transmitting frame information from a Base Station (BS) or an upper Relay Station (RS) to a lower RS in a multi-hop relay wireless communication system.
2. Description of the Related Art
In fourth-generation (4G) communication systems, radii of cells are reduced to achieve a higher transmission rate and accommodate a larger number of calls. Centralized network design with conventional technology is not viable for the 4G mobile communication systems. Thus, the 4G mobile communication systems should allow for distributed control and implementation, and cope actively with an environment change, such as addition of a new BS. For this reason, the 4G mobile communication systems should use a self-configurable wireless network.
Technologies used for an ad-hoc network are introduced to the 4G mobile communication systems for deployment of a self-configurable wireless network. A primary example is a multi-hop relay network configured by introducing a multi-hop relay scheme used for the ad-hoc network to a cellular network using fixed BSs.
Since communications are performed between a BS and a Mobile Station (MS) via a direct link, a highly reliable radio communication link can be easily established between them in the cellular network. However, the fixedness of BSs impedes flexible wireless network configuration, which makes it difficult to provide efficient services in a radio environment that experiences a fluctuating traffic distribution and a significant change in the number of calls.
To avert this problem, a relay scheme is adopted in which data is conveyed through multiple hops via neighbor MSs or neighbor RSs. A multi-hop relay scheme facilitates fast network reconfiguration adaptive to an environmental change and renders an overall wireless network operation efficient.
Also, the multi-hop relay scheme can provide an improved radio channel quality to an MS by installing an RS between the BS and the MS and thus establishing a multi-hop relay path via the RS. In addition, the multi-hop relay scheme can expand cell coverage because it can provide high-speed data channels to MSs in a cell boundary area where channel conditions from the BS are poor.
FIG. 1 illustrates the configuration of a wireless communication system using a conventional relay scheme.
Referring to FIG. 1, a first MS (MS1) 110, which is located within a service area (i.e., coverage) 101 of a BS 100, communicates with the BS 100 via a direct link. A second MS (MS2) 120, which is located outside the service area 101 of the BS 100 and thus is in poor channel condition, communicates with the BS 100 via a relay link of an RS 130.
That is, using the RS 130, the BS 100 can communicate with MSs that are in a poor channel condition because they are located outside the service area 101 of the BS 100 or in a shadowing area experiencing severe shielding effects from buildings.
In order to support a relay link using RSs, the wireless communication system using a relay scheme must perform communication using a structure illustrated in FIG. 2, which particularly is a frame structure for a wireless communication system using a conventional relay scheme.
Referring to FIG. 2, the frame is divided into a DownLink (DL) subframe 200 and an UpLink (UL) subframe 230. The DL/UL subframe 200/230 is divided into a first section 210/240 for a direct link service and a second section 220/250 for a relay link service.
The first section 210 of the DL subframe 200 includes a BS preamble channel 211, a control channel 213, and a traffic channel 215, for transmission from the BS through a direct link to an RS and an MS.
The second section 220 of the DL subframe 200 includes an RS preamble channel 221, an RS control channel 223, and an RS traffic channel 215, for transmission from the RS through a relay link to an MS.
The first section 240 of the UL subframe 230 is used to transmit control information and traffic data from the RS and the MS, which is connected through a direct link, to the BS. The second section 250 of the UL subframe 230 is used to transmit control information and traffic data from the MS, which is connected through a relay link, to the RS.
As described above, in order to support a relay scheme, the wireless communication system performs communication using the frame structure illustrated in FIG. 2. However, the frame structure of FIG. 2 supports only two-hop wireless communication systems because it has no section for RS-RS communication. Thus, the wireless communication system using a relay scheme needs a frame structure for supporting a multi-hop relay service.